Age related Macular Degeneration (AMD) is thought to be the leading cause of blindness in the elderly. It has been estimated that about 12 million people in the United States suffer from AMD. Macular carotenoid pigments, such as lutein and zeaxanthin, may play a role in the progression and/or onset of AMD. Carotenoids are from a family of natural pigments that are found in both plants and animals. Animals generally derive carotenoids from dietary sources such as green leafy vegetables and orange and yellow fruits and vegetables. Epidemiological studies have shown that there is an inverse correlation between high dietary intakes of carotenoids and blood levels of lutein and zeaxanthin and the risk of advance AMD. See Eye Disease Case Control Study Group, “Antioxidant status and neovascular age-related macular degeneration,” Arch. Ophthalmol (Chicago) 111, 104-109 (1993); J. M. Seddon, U. A. Ajani, R. D. Sperduto, R. Hiller, N. Blair, T. C. Burton, M. D. Farber, E. S. Gragoudas, J. Haller, D. T. Miller, L. A. Yannuzzi, and W. Willet, “Dietary carotenoids, vitamins A, C, and E, and advanced age-related macular degeneration,” J.Am. Med. Assoc. 272, 1413-1420 (1994).
It has been hypothesized that carotenoids may protect against AMD because of their free-radical-scavenging properties as antioxidants. The ocular tissue may be at high risk of oxidative damage because of high levels of light exposure. Carotenoids absorb light in the blue-green spectral range; therefore, carotenoids may act as filters that can attenuate photo-chemical damage and/or image degradation caused by short-wavelength visible light reaching the retina. See W. Gellerman; I. V. Ermakov, M. R. Ermakova, R. W. McClane; D. Y. Zhao, and P. S. Bernstein, “In vivo resonant Raman measurements of macular carotenoid pigments in the young and the aging human retina,” J. Opt. Soc. Am. A, 19, 6, 1172-1186 (2002).
Raman spectroscopy has been used to obtain spectra indicative of carotenoid pigments in the retina. See Id.; W. Gellerman; I. V. Ermakov, R. W. McClane, P. S. Bernstein, “Raman imaging of human macular pigments,” Optics Letters, 27, 10, 833-835 (2002). Lutein and zeaxanthin and other carotenoid pigments feature a Raman-active, π-electron conjugated carbon backbone with alternating carbon-carbon double (C══C) and single (C—C) bonds and strong electronic absorptions. Studies by these researchers reportedly used resonance Raman spectroscopy for the measurement of macular carotenoid levels in excised human eyecups from cadavers (Optics Letters 27, 10, 833-835 (2002)) and in living humans (J. Opt. Soc. Am. A. 19, 6, 1172-1186 (2002)). These studies reported a decline in the Raman signal correlated with increasing age. Id at 1183.
Despite the foregoing, there is a need for improved systems, methods, and devices for the non-invasive in vivo analysis of carotenoids in the eye.